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Agricultural Experiment Station. 


URBANA, DECEMBER, 1901. 


BULLETIN No 67. 


APPUE: SCAB, 


By GEORGE P. CLINTON, M.S., Assistant BOTANIST, BREICUL SERRE 
EXPERIMENT STATION. 


Investigations by the Department of Horticulture of the Uni- 
versity of Illinois upon the disease commonly known as Apple Scab 
were published in Bulletin No.54. These studies were mostly con- 
nected with preventive measures and the conclusions were mainly 
based upon field experiments. The present publication records the 
results of botanical studies made during the years 1898, 1899, and 
1900. 

Scab is a disease of the leaves and fruit of apples (Fig. 2) 
caused by a parasitic fungus botanically named Fusicladium 
dendriticum. Many fungi possess at least two stages ; namely, a 
summer or temporary spore stage adapted to spread the disease 
during the growing season of the host, and a winter or permanent 
stage adapted by greater protection afforded the spores to carry 
them through the winter and thus insure the infection of the host 

109 


IIo BULLETIN NO. 67. [December, 


again the following year. These stages usually differ greatly in 
appearance and may occur on different parts of the same host 
and at different times of the year, or they may occur on entirely 
different plants, thus causing one to regard them as two distinct 
species until their life history has been thoroughly worked out. 

The apple scab constitutes the temporary stage of a fungus 
and one of the points of investigation was to determine if there 
were a permanent stage connected with it, or, if not, how the fungus 
passed the winter. Accordingly careful examinations were made 
of the twigs and old fallen leaves during the fall and spring with 
the result that on the latter in the spring there was found a fungus 
that appeared to be the permanent stage. Germination of the 
spores of this in Van Tieghem cells in 1898 showed that the myce- 
lium from them could give rise to spores similar to those of the 
scab stage. This fungus had been long known to botanists but 
- under an entirely different name, being called Venturia chlorospora. 
At this time it was not known to the writer that the latter 
_ had been suspected by others as the permanent stage of the apple 
scab fungus. An examination of literature, however, showed that 
Goethe as early as 1887 had suggested the relationship of the scabs 
of pears and apples to mature stages on the dead leaves; that Bre- 
feld in 1891 figured a temporary spore stage obtained from a Ven- 
turia on pear that was similar to the leaf scab of that plant; and 
that Aderhold, 1894 and later, had made a very comprehensive 
study of the scabs of apple, pear, and cherry and had connected ~ 
them with species of Venturias that develop on the dead leaves of 
these hosts. 

From the results of these and the writer’s investigations there 
is no doubt that apple scab is merely a parasitic summer stage of 
a permanent saprophytic fungus occuring on the fallen leaves. It 
also appears to be this latter form that is largely (in its immature 
condition) responsible for carrying the fungus through the winter. 
At least the writer has been unable to find any satisfactory evi- 
dence that the scab stage persists on the young twigs, as has been 
stated by some investigators, and by means of a new crop of scab 
spores in the spring spreads the disease to the young fruit and 
leaves. Neither was there found any evidence that the old spores 
lived over the winter on the fallen leaves, or that the mycelium in 
these gave rise to a new crop for spring infection. 


INJURY. 


This is a common disease of the apple wherever grown though 
the amount of damage inflicted may vary considerably in different 


Igo0I.] APPLE SCAB. III 


localities and especially during different seasons. It occurs on the 
leaves usually in distinct, small, circular, olive colored areas and 
in time is likely to cause more or less puckering of the tissues 
or even killing the plant cells beneath. When very vigorous on 
young leaves it may cause them to turn yellowish and drop from 
the tree, though usually the leaves remain attached until fall when 
they may be shed somewhat prematurely. By these means the 
fungus interferes with their function as food producing agents and 
thus more or less indirectly affects the general health of the tree. 


On the fruit it produces the “‘scabby” spots familiar to every- 
one. These are roundish, olive-colored, roughish areas ‘usually 
about one quarter of an inch in diameter, or by coalescence more 
or less covering the surface of the apple. When the very young 
fruit is very badly infected it may cause distortion and interfere 
with the normal development in size, or, if severe enough, cause 
the young apples to fall from the tree. The injury of the fungus 
is thus direct and easier of determination. ’ 

By these direct and indirect effects the quantity of fruit pro- 
duced may be considerably lessened and the quality made inferior. 
It is hard, hcwever, to give the exact loss caused by such a disease 
unless one carries on careful experiments to determine quantity 
and quality of fruit produced from sprayed and unsprayed trees of 
the same variety grown under otherwise similar conditions during 
a series of years. Most estimates given from such losses are mere 
guesses. There can be no doubt, however, that thousands of dol- 
lars are lost each year even in this state alone, and that during 
certain years the loss is much greater. Professor W. J. Green, of 
Ohio, who has carried on careful spraying experiments against scab 
gives the following as results in an orchardin 1897: ‘The average 
per sprayed tree was 6.75 bushels and of the unsprayed 2.42. Fifty 
sprayed trees produced 4.33 bushels of apples more per tree than 
the unsprayed, which was secured at a cost of not more than 20 
cents per tree. In the case of the Northern Spy and Baldwin the 
actual profit derived from the treatment was more than $5.00 per 
tree.” 

This fungus, on the whole, seems to be more injurious in the 
states of the Mississippi valley than in some of the eastern coast 
states. Its injury, as stated before, also varies considerably dur- 
ing different years. This is largely due to weather conditions. It 
does most injury those years which have unusually wet springs, 
especially if cold damp weather’ occurs during the unfolding of the 
leaves. Its severity also seems to bear some relation to the amount 
of the Venturia stage that has developed on the old leaves. 


112 BULLETIN NO. 67. [ December, 


There appears to be no such thing asa scab-proof variety. 
Various writers have recorded .observations showing that certain 
varieties have been more severly injured than others and there is 
no doubt that this is the case. It is very likely that such differences 
are due in large part to the thinner or more easily punctured cuti- 
cle of the scabbier varieties. The writer has also observed that 
scab is a lover of neglected orchards—orchards which have not 
been properly sprayed, pruned, or cultivated—and that it seems to 
be less abundant on very young trees, especially where such trees 
areisolated. This latter is probably due to less favorable conditions 
for original infection. 

Scab has been known to botanists as a fungous trouble of the 
apple since the first part of the nineteenth century. Schweinitz, 
oue of the first collectors of fungi in this country, found it at work 
on Newton Pippins in New York and Pennsylvania in the early 
thirties of the past ceutury. Curtis records it as common on apples 
in North Carolina in 1867, and other early writers have listed it 
from various states. 

The earliest reference to its appearance in this state that has 
been found is a note in the Report of the Illinois Horticultural 
Society for 1863, page 119, where Mr. Murtfeldt, of Ogle County, 
reported Carolina Red June, and Early Red as small and inclined 
to scab. Professor Burrill in 1883 writing of it as an apple scourge 
in the Mississippi Valley, said in part: ‘‘ Everyone must have 
noticed last year a peculiar shriveling and curling of the apple 
leaves, beginning in many cases soon after the bursting of the buds 
in spring time and continuing more or less during the season. * * * 
The apples have been, in numerous instances, so scarred and spotted 
as to be practically worthless, except for stock or cider, * * * In 
Champaign County the Karly Harvest apples, among others, were 
divided half way to the core, or even deeper, by several irregular 
fissures, leaving knobby lobes, more or less covered by a layer of 
blackened corky tissue.” The writer in his collecting in recent 
years over the state has always found apple scab more or less com- 
mon and often doing serious injury. 


PREVENTION. 


It is not the purpose of this bulletin to go into detail concern- 
ing the prevention of thisdisease. It is known, however, that the 
injury can be stopped largely by proper attention to spraying. 
Since the experiments started under the direction of Galloway, of 
the U. S. Department of Agriculture (by Goff in Wisconsin and by 
_ Taft in Michigan) there has been much written by various station 


ST eee 


1901. | APPLE SCAB, 1I3 


workers concerning the prevention of scab through spraying. Asa 
result of these activities Bordeaux mixture has been found the most 
valuable fungicide. The present tendency is touse it made as fol- 
lows : 41b. copper sulphate, 4lb. fresh lime, and 50 gal.water. The 
copper sulphate may be dissolved in hot water, the lime slaked in a 
suitable quantity of water, the two then being mixed together and 
strained into a barrel containing the remaining amount of water. 

Much of the success in the use of a fungicide depends upon 
the proper application and the time of spraying. The trees 
should be thoroughly sprayed. The first application should be 
made soon after the leaves begin to unfold, followed by a second 
soon after the petals begin to fall and by a third in less than 
two weeks if the season has been favorable for the development 
of scab. Later sprayings are apt to burn the foliage and russet 
- the fruit and so are not very desirable. Some writers advocate 
two sprayings before the petals fall, the first with the swelling of 
the buds and the second after the leaves have expanded but before 
the petals are open. Winter spraying with a strong solution of 
copper sulphate has also been found to retard the first appearance 
of scab, but it is questionable if it is worth the extra expense and 
trouble if the first treatment with Bordeaux mixture is made 
promptly and thoroughly. Incase the codling moth is injurious 
Paris green, at the rate of 1 lb. to 200 gal. of the Bordeaux mixture, 
may be added for the second and third sprayings. 

Besides spraying proper attention should be given to pruning, 
as properly pruned trees are more easily and cheaply sprayed and 
also because unpruned trees afford greater protection against quick 
evaporation of moisture and thus so far favor infection by scab. 
The same holds true of proper cultivation, since orchards neglected 
in this respect offer greater protection to the fallen leaves, which, 
as we have seen, are the means by which the permanent stage de- 
velops and produces infection in the spring. No careful experi- 
ment of raking together and burning all of the fallen leaves from 
an orchard has been carried on and so nothing definite can be said 
of the advantage of this procedure. However, in a small plat 
in an orchard from which the leaves had been so removed the first 
appearance of scab on those trees seemed to have been retarded and 
reduced. Such work to be of any value should be done very thor- 
oughly in the autumn after all of the leaves have fallen. 


, FUSICLADIUM OR PARASITIC STAGE. 


TIME oF APPEARANCE, ETC.—Scab makes its first appearance 
early in the spring, usually soon after the leaves begin to unfold, 


114 BULLETIN NO. 67. [ December, 


and it is while these and the fruit are in a young condition that the 
fungus can best infect them. While it is to be found from the 
first appearance of the leaves until they drop off in the fall, there 
are two periods of greatest activity in spreading, one early in the 
spring and of the greater importance and the other in the autumn. 
This latter infection does little damage but is important because it 
is probably largely responsible for the development of the mature 
stage. 


During the years 1898 to 1900 a careful watch was kept of 
apple trees to determine first appearance, manner of infection, and 
relative abundance of scab. In 1898 the first sign of scab was 
seen on May 2d, though from its condition then it probably made 
its appearance several days earlier. At this time the oldest leaves 
had not reached their full size. On some trees the scab appeared 
more abundant on the lower than on the upper branches ; it was 
much more abundant on those leaves developed from flower buds 
than on those from the later purely leaf buds ; it was most abun- 
dant on the lower surface in the vicinity of the midrib. This lat- 
ter condition showed that the first infection had taken place very 
early, before the leaves were entirely unfolded. As apple leaves 
are folded on the midrib as an axis with the upper side within and 
the edges somewhat involute, the lower surface next the midrib is 
the first and most exposed part. The fact that the scab was 
most abundant on the leaves produced from flower buds sug- 
gests the possibility of insects as carrying agents for the spores, or 
it might be that such leaves being the first to unfold merely show 
the scab earlier on this account. On the very young fruit the scab 
often appeared at one side and toward the blossom end. The 
spring was cold and damp and as a result scab was much worse 
this year than either of the other years. There was also found an 
abundance of the Venturia stage on the old leaves before and dur- 
ing the first appearance of the scab. 


In 1899 a very careful examination showed the first scab ‘on 
May 5th, on a very few leaves. This year it was slow in appear- 
ing and the oldest leaves escaped more than the later which were 
developed during a more moist period. The scab also appeared 
mutch more commonly on the upper sides of the leaves. The early 
spring was unusually warm and dry and therefore very unfavor- 
able for the spreading of the disease. The Venturia stage was 
also much later in developing and many perithecia were found 
which seemed never to have matured their spores. This stage was 
much scarcer than it was the previous year. 


In 1900 the first sign of scab was found on a crab apple on 


1901. ] APPLE SCAB. 115 


May 11th. This tree had beeu badly infested the previous year, 
and when first examined only two or three scabby leaves were 
found. The fungus did not make a general appearance in orchards 
until quite late, the latter part of the month. In one orchard ex- 
amined on May 21st no scab was found on a certain tree. ‘This 
was examined again on June 4th and found badly scabbed on most 
of the lower leaves except the oldest. This tree had branches that 
reached down to the ground. The orchard was uncultivated and 
that spring the Venturia stage had been found fairly common on 
the old leaves. ‘The following counts of leaves taken as they came 
show the relative abundance of scab on the lower and upper 
branches of the tree: 


Total leaves examined. Scabby. Total scabby spots. 
Branch in top 118 3 3 
Branch on ground 99 53 520 


A later examination showed that the scab had spread some- 
what in the top of the tree. These conditions seem clearly to in- 
dicate that the original infection had come by means of the lower 
branches from the Venturia stage on old leaves on the ground. 

Often the primary infection seems to be slight and in such 
cases it is from the spores developed from these that the scab be- 
comes spread over the tree. Sometimes it seems to appear on one 
tree and spread from this to the others. Very often trees show no 
difference in the development of scab on different parts. | 

ON THE LEAVES.—Scab generally occurs in roundish colonies 
about one quarter of an inch in diameter (Fig. 4). These may re- 
main entirely distinct or run together so that they loose their in- 
dividuality. This is often the case where they are crowded along 
the prominent veins, It is a common thing for the colonies to 
start over the veins as if these offered more favorable places for in- 
fection or for growth. The spots have an olive green color and 
under a magnifier are seen to consist of distinctly toothed and 
branched fungous strands (apparently on the surface of the leaf) 
that radiate from a common center. 

Sections through scabby spots seen under the microscope show 
the mycelium as a single thread in thickness (but no doubt several 
lying side by side) creeping over and closely applied to the top of 
the epidermal cells but beneath the cuticle and narrowing down at 
the end to a point by means of which it separates the cuticle from 
the epidermal cells (Fig. 7). The cuticleon the young leaves is not 
very easily made out but on the older ones where it has attained 
some thickness it becomes more evident. By this manner of devel- 
oping the fungus is protected on the outside by the cuticle while 


116 BULLETIN NO. 67. [ December, 


by being directly applied to the cells on the inner side it is able to 
take nourishment by absorption; no haustoria were found. The 
mycelium sometimes pushes down somewhat between the epider- 
mal icells,but very rarely, if ever, goes deeper in green leaves. 

When this subcuticular mycelium, which averages 4 or 5 in 
diameter, is ready to form spores it divides up into more or less 
distinct, hyaline, roundish cells about the same diameter as the 
threads (Fig. 8 and 9). Often there is but a single layer of these, 
but sometimes, especially above veins and woody tissue, this sub- 
hymenium is:two or more cells deep. From these are developed 
upright at first bluntly lanceolate to ovate shaped cells, or corfidio- 
phores, that penetrate the cuticle (Fig. 6). They havea thicker, 
reddish, outer wall and a very thin hyaline inner one, and occur in 
groups of greater or less extent, generally touching each other a 
their broader bases but separated at their apices. 


The spores are formed by the protrusion from the apex of the 
conidiophore of its inner wall and contents as a hyaline roundish 
body, with more or less of a distinct base (Fig. 7and8). This, when 
fully grown, forms the lanceolate, acute, reddish olive colored 
spore. When mature the spore is pushed off by the development 
in a similar manner of a second one. Each time a spore is formed, 
however, the conidiophore is lengthened by the remaining short 
basal part. This at first consists of only the hyaline inner wall, 
but develops with the spore the outer colored wall. By this means 
the conidiophore is not only lengthened but given a banded appear- 
ance something like short joints of an extended sliding tube (Fig. 
10). The conidiophores thus in time become cylindrical with short 
swollen bases, their final length being determined by their age and 
the character of the season as affecting the number of spores 
formed. The old conidiophores sometimes develop a septum or 
two. On an apple leaf gathered the latter part of June there was 
seen a conidiophore that had developed ten of these spore bands. 


The scab colony soon assumes its full size and the chief change 
during the season is the development of some new conidiophores 
and the growth of the old ones. Toward the end of the season the 
cells of the subcuticular mycelium may increase somewhat in size 
and become more or less tinted, but the chief change in this respect 
comes after the leaves fall and their tissues die. Earlier or later in 
the season the action of the subcuticular mycelium, possibly in part 
through pressure, but probably largely through irritation, causes 
a more or less complete collapsing of the epidermal cells. This 
no doubt causes the puckering often seen on badly scabbed leaves. 

Scab spores are chiefly lanceolate, varying from narrowly 


1gO1.] APPLE SCAB. 


lanceolate to ovate (Fig. 16). They are widest near the base 
which tapers somewhat to the truncate end or former point of at- 
tachment. Toward the usually acute apex they taper gradually, 
but are sometimes slightly constricted giving a somewhat fiddle 
shape. Usually they are one-celled, though a septum is somtimes 
developed near the center. In color they are reddish olive and in 
size generally vary from 12—22 » in length by 6—9 / in greatest 
width. 

On THE FRuit.—-On the apples the fungus produces the so- 
called ‘‘scabby” spots (Fig. 5) which are usually % to % of an 
inch in diameter though by coalesence they may more or less cover 
the surface. These develop vigorously on the very young fruit but 
after the apples obtain some size their growth is slow and usually 
there is little danger from further serious infection. This is 
due to the very thick cuticle developed on the fruit. The scab 
colonies when fresh have a dark olive green color with, usually, a 
narrow lighter horder. ‘The cuticle of the apple becomes ruptured 
and flaked off, and in time the olive colored fungous cells are also 
more or Jess worn away so that the color may assume a reddish 
brown shade due to the exposed dead tissues. 


Sections under the microscope show that the development of the 
fungus is somewhat different from that on the leaf. This and the 
microscopic appearance caused botanists originally to consider the 
forms on the leaf aid fruit as two distinct fungi. The difference 
is not so great as it appears and is due chiefly to the greater de- 
velopment on the fruit of the subcuticular mycelium which in the 
more advanced stages often forms a tissue many cells deep (Fig. 
15d). This vigorous development seems to be due to the very ° 
thick cuticle (Fig. 13c) which evidently makes it much more diffi- 
cult for the penetration of the fungus to the outside (Fig. 14) and 
as a result there is formed quite a tissue before the conidiophores 
are pushed through and developed. While at first this subcuticu- 
lar mycelium is made upof the small, roundish, hyaline cells 
these grow in size and especially at the outer surface become more 
or less colored like the conidiophores. In the apple stored over 
winter, shown in Fig. 15, these cells had all become thus colored 
and gave the appearance of a resting stage of the mycelium. The 
action of the fungus often causes more or less of a collapsing or 
flattening of the host cells beneath and this results in the forma- 
tion of a sort of corky tissue (Fig. 12b) which affords protection 
to the plant against evaporation and the entrance of other fungi. 


Scabby apples that have remained outdoors all winter, because 
of the general rotting produced by other fungi, show little evidence 


- 


11d BULLETIN NO. 67. [December, 


of scab and there is no ground for supposing that they are the 
means of any spring infection. Stored scabby apples, having been 
protected against decay, show some evidence that the mycelium at 
the margins of the colonies is still alive and capable of producing 
a few spores. 


ON THE TwIGs, ETC.—It has been claimed by some botanical 
writers that the apple scab fungus also developed on the young 
twigs and by this means was carried over the winter and by the pro- 
duction of scab spores in the spring caused the infection of the 
leaves and fruit. During the three seasons the writer has had the 
fungus under observation very careful examinations have been 
made of the twigs at different times of the year to determine if 
this was the case. In only one instance was the fungus ever found 
growing on the branches and that exception was a badly infected 
crab-apple which had several twigs of the current year’s growth 
considerably infected. On this tree the scab was also found abun- 
dantly on the leaves and petioles and in a few cases on the pedicles, 
calyces and styles. The tree was thoroughly examined again the 
next spring but no sign of the fungus was found on the twigs. It 
is not uncommon for the scab to occur on the leaf petioles but it 
never seems to develop down upon the twigs in such cases. In the 
spring, before the appearance of the fungus, loose spores have been 
scraped from the twigs, but it appears hardly probable, if alive, 
that these are the means of any considerable infection. 

GERMINATION OF SporES.—F resh spores placed in waterin Van 
Tieghem cells generally show some beginning to germinate inside 
of twelve hours and by the end of twenty-four hours these may have 


* germ-threads several times the length of the spores (Plate I, Fig. 


A). The germ-thread may emerge from either end or the sides of 
the spore but it most frequently comes from the pointed or apical 
end. Usually the germination does not proceed further than to 
form a simple, rarely slightly branched, hyaline, septate thread 
somewhat narrower than the spore and often many times its 
length. 

In apple leaf broth or apple leaf agar the germination is much 
more vigorous, the germ-threads often becoming branched and more 
elongated, forming a slight mycelium. Often the ends of the 
threads or branches become somewhat swollen, more closely septate, 
and develop short, more or less knobbed, or irregular branches that 
when cut off by a septum in some instances have a spore-like ap- 
pearance. These peculiar tips usually become tinted like the spores 
(Plate II, Fig. A). Their nature is not very evident. They may 
possibly be only a sort of resting condition of the mycelium since 


190I.] ; APPLE SCAB. II9 


frequently they send out more slender hyaline threads as if in ger- 
mination (Plate II, Fig. C) and these again may develop similar 
tips. Occasionally in these cultures the mycelium formed true scab 
’ spores. These are usually produced on short hyaline side branches 
not especially differentiated as conidophores. The first spore formed 
may be pushed aside by the development of a second and often 
several are seen detached in the neighborhood. ‘These spores are 
colored and otherwise similar to those produced in nature (Plate I, 
Fig. D). 

ARTIFICIAL CULTURES.—The writer usually found it rather 
difficult to obtain cultures of the scab fungus from Petri dish sep- 
aration cultures of the spores. This was partly due to frequent 
development of surface bacteria over the agar, especially on fresh 
apple leaf agar, but chiefly to the very slow development of the 
scab colonies compared with those of the molds whose spores had 
been introduced. It usually took from two to four or five days be- 
fore the scab colonies could be detected by the naked eye. These 
then showed as very small lax growths entirely embedded in the 
medium but with time increasing in size and growing somewhat 
into the air. These colonies when very young could be traced down 
to the spores. Figure 17 shows in part the mycelium of one of 
these colonies still attached to the spore. Such colonies while 
young were transferred to test tubes of old apple leaf agar, new 
apple leaf agar, beef broth agar, beef broth gelatin, beef broth, beef 
broth corn meal, old apple leaves, and young apples. The growth 
in these media differed somewhat, chiefly as follows: 


ON OLD APPLE LEAF AGAR.—The colonies were about ¥ to % inch in diam- 
eter and composed of a very prominent dense growth of dirty white threads into 
the air. Spores were rarely found and these disappeared through germination 
(Fig. 23). 

On NEW APPLE LEAF AGAR.—The chief difference between this and the 
above was the more prolific development of spores and the somewhat slighter 
growth of threads into the air. 

On BEEF BrotTH AGAR.—-This medium being lighter colored than either of 
the above showed a dark growth in the agar. There was also a slight growth of 
dirty white threads in the air. Spores were produced somewhat, at least at first. 
(Fig. 22). 

ON BEEF BROTH GELATIN.—The growth in the medium was very dark and 
in striking contrast to it, while the growth in the air was very slight. Spores were 
found but usually disappeared through germination. (Fig. 25). 

In BEEF BrotTH.—The growth was confined to the liquid or sides of the tube 
at surface and was similar to that in the gelatin. (Fig. 24). 

On BEEF BROTH CORN MEAL.—On this medium the growth most nearly ap- 
proached the appearance in nature. A dense, short, olive green felt developed on 
the surface with no growth of dirty white threads in the air. Spores were pro- 
duced very abundantly and did not disappear through germination. (Fig. 26). 


120 BULLETIN NO. 67, [December 


ON YOUNG STERLIZED APPLES.—The growth usually was not very vigorous 
and was chiefly at place where agar was introduced with the mycelium. In some 
cases the dirty white threads spread out over the apple but caused no scab like 
appearance. 

ON OLD STERLIZED APPLE LEAvES.—The growth here was also chiefly in 
the region of the introduced agar forming more or less of a prominent tuft of dirty 
white threads which ran out somewhat on surface of leaf (Fig. 21). Growths on 
old leaves were tried in the hope that the Venturia stage would be developed but 
were not.successful in this respect. While these cultures were unsuccessful, in 
the case where lately fallen apple leaves containing fine colonies of scab were 
placed in test tubes on moist cotton plugs and left until the next year the Venturia 
perithecia were found abundant though immature. 

The mycelial threads of cultures are first hyaline but in time 
become tinted especially those in the medium or against the glass 
of the test tube where they often assume a dark olive green color. 
They vary in diameter chiefly from 2% » to 5 and have at first 
uniform or vacuolate protoplasmic contents (Fig. 19), but in time 
are apt to be more or less filled with highly refractive granules of. 
varying sizes (Fig. 18). In the young threads the cells are com- © 
paratively longer than in the older, broader ones. In the latter 
there may occur circular swellings as if due to vigorous osmotic 
action (Fig. 20; Plate II, Fig. Bc). In old dried out cultures highly 
refractive spore-like bodies, which may possibly have served as 
chlamydospores (Plate II, Figs. E, F) were sometimes found. 

ARTIFICIAL INFECTION.—Because of the general presence of 
scab on apple trees artificial infection of leaves out doors is not safe 
unless on isolated trees not liable to develop scab. Most of the 
experiments tried were with one or two year old seedlings planted 
in crocks and kept in doors at a higher temperature than the out- 
side. In such cases the spores were usually sprayed in water on the 
leaves, (especially when they were very young) and the moisture 
prevented from evaporating by covering the trees for a few days 
with bell jars lined with moist paper. For some reason it was 
found rather difficult to infect the leaves of such trees, though the 
conidial stage of the powdery mildew had no difficulty 1n producing 
natural infection. Out of the various trials made at different times 
less than half of the trees produced leaves with scab and never with 
any abundance. In one instance where very young leaves were 
sprayed on three successive days with water containing spores 
and kept for ten days under a moist bell jar there were eventually 
found only three leaves with a total of five scab colonies. In those 
cases where colonies developed they were usually first seen about 
three weeks after the spores had been put on the leaves. The ex- 
periment was also tried of spraying spores on the unfolding leaves 
of different varieties of apples whose twigs had been cut off and 


1901. ] APPLE SCAB. 121 


placed in water under bell-jars but no results were obtained in 
these cases since the leaves all dropped off by the end of two weeks. 


VENTURIA OR SAPROPHYTIC STAGE. 


On Deap Leaves.—After the scab infected leaves fall from 
the trees in the autumn and lose their green color the subcuticular 
mycelium slowly changes. The rounded cells become larger 
(eventually 5—10 » in diameter) and gradually tinted to a reddish 
olive color and also give rise to similarly colored mycelial threads 
that penetrate into the interior of the leaf. In sections made of 
fallen leaves gathered in October there were seen signs of the for- 
mation of perithecial bodies and occasionally threads could be 
traced connecting these with the subcuticular cells. The perethe- 
cia generally originate in the loose part of the leaf a short distance 
above the lower epidermal cells, and while still young show an 
outer covering of colored cells and a few inner hyaline ones. 

The Venturia stage is thus produced from the mycelium of the 
scab stage, the dead leaves allowing easy penetration into the 
interior and offering no hindrance to further development. From 
the fact that the perithecia most frequently occur on the lower side 
of leaves and are not found unusually abundant on or near con- 
spicuously scabby spots, it seems quite probable that the less con- 
spicuous scab colonies originating in the fall on the under side of 
the leaves are largely responsible for the development of this stage. 

The relationship of these two forms is well shown by the fol- 
lowing data obtained regarding their development. 

May. Scab first appears on young apple leaves and fruit and during this 
month and June obtains its greatest foothold. 

July to September. The warm, generally dry, weather is not very favora- 
ble for spreading the disease to the leaves, and fruit usually suffers but little from 
further infection. 

September and October. Scabappears to develop somewhat more abundantly 
especially on the lower surfaces of the leaves, but not necessarily in vigorous 
fruiting condition. ; 

October and later. On the fallen dead leaves there are signs of the forma- 
tion of the perithecia of the Venturia stage. 

October to April. Perithecia slowly develop as weather conditions prove 
favorable. 

April and May. Perithecia with mature ascospores'are now found. 

June. Venturia stage disappears. 

The Venturia stage was found most abundant the spring of 
the year apple scab was the worst. After one severe winter it was 
apparently injured by the cold since many of the perithecia never 
came to maturity. It was never found on any other leaves than 
the apple and succeeded best where these were protected by sod, 
especially where more or less heaped together in fence corners. 


122 BULLETIN NO. 67. [ December, 


The perithecia show on the leaves as small black pustules gen- 
erally scattered but sometimes congregated in small groups often on 
greyish spots which may mark the place of the fall scab colony. 
They frequently occur in the vicinity of the veins. Sometimes 
they are found on leaves that show no sign of scab to the naked 
eye.: When mature they are more or less loosely imbedded in 
the leaf tissues and at the time of their disappearance infected 
leaves often show numerous small holes where they had been im- 
bedded. The writer has never found them upon the old fruit and 
only once on the twigs and in this case the single large perithecium 
was probably blown there. 

MicroscoPicAL APPEARANCE.—F rom the examination of va- 
rious specimens the microscopical characters may be given as fol- 
lows: Perithecia when mature very dark, light scarcely shining 
through unless crushed and then showing outer wall of dark olive 
green color, spherical or subspherical, generally 90—150 » in 
diameter ; reticulations (Fig. 27) not evident until perithecia are> 
crushed, irregularly polygonal, 5—15 »; ostiolum showing at first 
as a lighter spot, usually on a broad somewhat beaked projection 
(Fig. 29 and 30); bristles (Fig. 28) absent or surrounding the pro- 
jection, six or more in number, easily detached, of same color as 
perithecium, simple, tapering somewhat from base to apex, usually 
about 35 » though varying at least from 25—75 yin length; asci 
(Fig. 27; Plate III, Fig. A) numerous, at least when mature with- 
out paraphyses intermixed, without very evident stipe, oblong to 
spatulate, frequently slightly curved, 55—75 » x 6—12 4; spores 
(Fig. 27; Plate III, Fig. B) eight in an ascus, upper single ranked, 
lower irregularly two ranked, two celled with ratio of length of 
cells about 2:3, oblong, with upper cell usually slightly wider than 
lower, light reddish or olive brown, 11—15 » x 5—7 ». 


GERMINATION OF SporES.—Spores when placed in water in 
Van Tieghem cells germinate rather abundantly within the first 
twenty-four hours. They become considerably swollen and then 
send out a germ-thread from one or both cells, but most frequently 
only from the lower cell. While these threads may originate from 
any part of the cell they usually come from the free end. They at- 
tain a length several times the length of the spore, taper somewhat 
toward free end and become septaté at the base (Plate III, Fig. FE). 


In apple leaf agar the germination was more vigorous with 
the production of the curiously enlarged and irregularly knobbed 
or branched tinted tips (Plate IV, Fig. C) that were also produced 
in cultures from scab spores. In one culture the mycelium also 
gave rise to true scab spores (Plate IV, Fig. D). 


I19OT. ] APPLE SCAB. 123 


ARTIFICIAL CULTURES.—Colonies were produced from spores 
in Petri dish separation cultures like those from scab spores, small, 
lax, and of slow development. So far as tried the growths on va- 
rious media were similar to those of the scab stage. The fungus 
did best on apple corn meal where it produced characteristic 
threads and spores of scab. 

The culture work with this stage was not carried on very ex- 
tensively because of the difficulty of finding spores in 1899 and be- 
cause in 1900 much of the time during the season of the fungus 
was spent working with another fungus supposed to be probably 
. an immature condition of the Venturia. This was finally seen to 

be Spherella and was determined by Ellis as Spherella pirina, BK. & 
EK. This fungus also is found on the dead leaves, apparently quite 
- common. It occurs most abundantly upon the upper surface and 
produces more or less grouped perithecia that are smaller and 
originally not so deeply imbedded in the leaf as those of the Ven- 
turia. The mature perithecia also lack the bristles that are 
usually present with the Venturia and the spores differ in being 
smaller and hyaline. 

IpEnTITY.—The apple leaf Venturia has been commonly called 
Venturia chlorospora (Ces. ) Karst., which name was also made to in- 
clude various forms on the fallen leaves of other hosts, such as Salix, 
etc. Aderhold has recently shown that these forms are distinct, 
even those occurring on the closely related hosts pear and cherry 
being different species from that on the apple. For this latter 
form he has adopted the name Venturia inequatis (Cke.) Ad., using 
the specific name first applied by Cooke. The latter de- 
scribed this as a new species, Spherella tnequalis, in Seem. Journ. 
Bot. in 1866, Niessl in 1881, Rabenhorst’s Fungi europaei no. 
2663, placed this species under the genus Didymospheria as VD. 
tnegualis (Cke.) Nessl. Winter, instead of Aderhold, seems to 
have been the first to place the species under the genus Venturia 
as the specimens on apple leaves distributed in 1880 in de Thu- 
men’s Mycotheca universalis no. 1544 are called Venturia tnequa- 
lis, Wint. in litt. 


NOMENCLATURE. 


Fries was probably the first botanist to give a name to apple 
scab. About 1819 in Nov. Fl]. Suec. he applied the name SZzlocea 
Pomi to the fructigenous form. In his Syst. Myc. in 1829 he also 
described this species and this is the reference for the name usually 
given by botanists. On the same page of this latter work he de- 
scribed a fungus on the leaves of apple and pear that to the writer 


a 


124 BULLETIN NO. 67. [ December, 


seems to be the leaf form of scab, though Sfzlocwa epiphylla is 
never given as one of its synonyms. Persoon in 1822 under the 
name /umago Mali also described a fungus on the leaves of apple 
that by some botanists has been questioningly referred toscab. In . 
1833 Wallroth unquestioningly found the leaf form and named it 
Cladosporium dendriticum. Fuckel in 1869 placed this under the 
genus Fusicladium and since that time scab has been commonly 
called Husicladium dendriticum (Wallr.) Fckl. In 1834 Schweinitz 
described a new species on Newton Pippin apples from this country 
under the name of Dothidea pomigena.* 'This has been considered 
by some botanists as probably another name for the fructigenous 
form of this fungus. The writer was inclined to this view and so 
recently examined Schweinitz’s specimen in the Herbarium of the 
Philadelphia Academy of Science. While the specimen was in 
poor condition it was seen that it was not scab, being more like the’ 
fly speck fungus in its macroscopic appearance. Schweinitz, how- 
ever, did list apple scab from this country under the names S?/- 
ocea fructigena or S. Pomi. _He seems to have originated the 
name /ructigena though from his reference one would suppose that 
Fries was authority for it. The specimen in the Schweinitz col- 
lection is labeled Spzlocea Pom. In 1851 Bonorden described a 
scab fungus under the name of Fusicladium virescens. ‘There is 
some doubt whether this is a synonym of the apple or the pear 
scab. Bonorden gives apple as the host for his fungus but his 
figures more nearly resemble the scab of the pear, and so some 
botanists give it as a synonym of this. The last person to give a 
new name to this fungus was de Thiimen who, in 1875, described 
the form on the fruit as Vapicladium Soraueri. 

Since it has been clearly shown that scab is merely a stage of 
a Venturia it must now be named under that genus instead of 
under Fusicladium. Venturia ineqgualis (Cke.) Wint., seems an 
appropriate name, though some botanists would use for the spe- 
cific name the one first given to any of the stages of the fungus, 
which in this case is Pomz. Another possible objection against 
the use of the above name is that Cooke’s Spherella inequalis also 
included the form on the pear, which is now considered a distinct 
species. 

The different names applied to the scab stage, as found by the 
writer, are as follows: 


Spilocea Pomi, Fr. Nov. Fl. Suec. 5:79. 1819. 
? Fumago Mali, Pers. Myc. Eur. 1:9. 1822. 


*Sturgis (Am. Rep. Conn. Agr. Exp. Stat. 21:171) thinks that this descrip- 
tion applies to what he calls the Sooty Blotch fungus. 


1901. } APPLE SCAB. 125, 


? Sprlocea epiphylla, Fr. Syst. Myc. 3: 504. 1829. 

Cladosporium dendriticum, Wallr. Fl. Crypt. Germ. 1°: 169. 
1833. 
Spilocea fructigena, Schw. N.A.F.:297. 1834. - 
? Fusicladium virescens, Bon. Handb. Alig. Myk.:80. 1851. 
Fusicladium dendriticum, Fckl. Symb. Myc. : 357. 1869. 
Napicladium Soraueri, Thim. Hedw. 14 : 3-4. 1875. 
Fusicladium dendriticum £. Pyri Mal, 'Thtim. Myc. uni. no. 
1174. 1878. 

Fusicladium dendriticum, vat. minor. Sacc. fungi Ital. f. 782. 
1881. . 

Fusicladium dendriticum var. Soraureri, Sacc. Syll. Fung. 
4: 346. 1886. 

fusicladium dendriticum forma microsperma, Roum. Fungi 
sel. exs. no. 5592. 1890. 


EXSICCATI. 


Fusicladium dendriticum (Wallr.) Fckl. has been distributed 
in a number of different exsiccati of which the following have been 
examined by the writer and found to be this fungus: 

Spilocea Pomi, Fr. on apple fruit. Scler. Suec. exs. no. 260. 

Cladosporium dendriticum, Wallr. on apple leaves. Herb. 
crypt. belg. no. 695. 

Cladosporium dendriticum, Wallr. on Pyrus Malus. Klotz. 
herb. viv. myc, no. 1883. 

Cladosporium dendriticum, Wallr. on leaves Pyrus. Klotz. 
herb. viv. myc. II. no. 766. 

Napicladium Soraueri, Thiim. on apple fruit. Thtm. Myce. 
uni. no. 91. 

Napicladium Soraueri, Thiim. on apple fruit. Roum. Fung. 
sel. Gall. exs. no. 154. 

Fusicladium dendriticum forma microsperma, on leaves of 
apple. Roum. Fung. sel. exs. no. 5592. 

Fusicladium dendriticum f. Pyri Mali,on leaves Pyrus Malus. 
Thim. Myc. uni. no. 1174. 

Fusicladium dendriticum (Wallr.) Fckl. on leaves Pyrus 
Malus. Sey. & Earle Eco. Fungi no. 38. 

Fusicladium dendriticum (Wallr.) Fekl. on fruit Pyrus Jo- 
wensts. Sey. & Earle Eco. Fungi. no. 420. 

Fusicladium dendriticum, Wallr. on leaves Pyrus Malus. Ell. 
N. A. F. no. 372b. 

Fusicladium dendriticum (Wallr.) on leaves Pyrus Malus. 
Ell. & Ev. Fungi. Col. no. 464, 


7 


126 BULLETIN NO. 67. [December, 


Fusicladium dendriticum (Wallr.) Fckl. on leaves Pyrus 
Malus. Briosi & Cavara Fung. par. no. 140. 

Fusicladium dendriticum (Wallr.) on leaves Pirus prunifolia. 
Rab-Wint-Paz. Fungi eur. no. 3997. 

Besides these there were found a number of specimens distrib- 
uted on Crategus and Sorbus tinder various names that have the 
appearance of this fungus, but which were not included with the 
above because of lack of knowledge concerning their permanent 
stage. 


BIBLIOGRAPHY. 


Apple scab has been the subject for much writing on the part 
of botanists and horticulturists. This is due to its wide distribu- 
tion and the considerable injury that it causes. Much of this 
literature relates to experiments for the prevention of its ravages, 
especially by the use of fungicides. The following references 
relate to articles and notes that the writer has indexed from his 
examination of such literature as was at his disposal. No doubt 
many more references could be added to the list: 


Aderhold, R. Die Perithecienform von Fusicladium dendriticum (Venturia 
chlorospora f. Mali). Ber. Deutsch. Bot. Ges. 12: 338-342. 1894. 
Shows the relationship between /. dendriticum on living apple leaves and — 
V. chlorospora {. Madi the permanent stage on the dead leaves. 


Aderhold, R. Litterarische Berichtigung zu dem Aufsatze ueber die Perithecien- 
form von Fusicladium dendriticum, Wallr. Ber. Deutsch. Bot. Ges. 13: 
54-5. 1895. 

Speaks of earlier investigations connecting Fusicladium dendriticum with 
Venturia stage. 


Aderhold, R. Die Fusicladien unserer Obstbaume. Landw. Jahrb. 25: 875 - 
914. 1896. [Illustr.] /ézd. 29 : 541 - 587. Igo0. [Illustr.] 
Gives detailed accounts of the scabs of apples, pear and cherry and shows 
their relation to Venturia stages on dead leaves of these hosts. 


Aderhold, R. Revision der species Venturia chlorospora, inequalis und ditricha 
autorum. Hedw. 36: 81. 1897. [Illustr.] 
Describes the different species of Venturia and gives their hyphomycetous 


stages, placing Fusicladium dendriticum under Venturia inegualis (Cooke) 
Ad. t 


Alwood, W. B. Fusicladium dendriticum. Virg. Agr. Exp. Stat. Bull. 24:24. 
1893. 
Mentions this as cause of one of the serious apple diseases in this state. 


Andre, Ed. Les Fusicladium et nos Vergers. Rev. Hort. 60:246. 1888. 
Gives short description of apple scab. 


Anon. Apple and Pear Scab. N. Y. Agr. Exp. Stat. Bull. 35:606-7. 1891. 
Describes briefly effect of fungus and recommends preventive treatment by 
spraying. 


190I.] ‘APPLE SCAB, 127 


Anon. Treating Apple Orchard for Scab. N.Y. Agr. Exp. Stat. Bull. 84: 19 - 20, 
31-33. 1895. . 
Recommends time for spraying and notes varieties injured by Bordeaux mix- 
ture. 

Anon. Apple Scab. Year Book, U.S. Dept. Agr. 1894:577. Jbid. 1895 : 587. 
bid. 1896 :625. bid. 1897 : 673. 
Gives treatment for prevention of scab. 

Arthur, J. C. Apple Scab and Leaf Blight. Ann. Rep. N. Y. Agr. Exp. Stat. 
3:370. 1885. 
Gives short note on damage caused by this fungus. 

Bailey, L. H. Scab-proof Apples. Gard. & For. 5: 442. 1892. 
States that there is no matketable scab-proof variety,—Baldwin the least 
susceptible. 

Bailey, L. H. The Recent Apple Failures. Corn. Agr. Exp, Stat. Bull. 84:58 - 
63, 66-8. 1895. [Lllustr.] 
Attributes apple scab as chief cause of failures and discusses the fungus and 
methods of combating it. 

Beach, S. A. Wood Ashes and Apple Scab. N. Y. Agr. Exp. Stat. Bull. 140: 
665-90. 1897. 
Reports experiments of applying wood ashes to the soil as not preventing 
scab. 

Beach, S. A. and Paddock W. Apple Scab. Ann. Rep. N. Y. Agr. Exp. Stat. 
14:345-7. 18096. 
Discuss briefly apple scab and prevention by Bordeaux mixture. 


Beach, S. A., Lowe, V. H., and Stewart, F.C. Scab. N. Y. Agr, Exp. Stat. 
170:385-7. 1899. 
Give short account of life history and methods of prevention. 

Berkeley, M J. Why Do Pears and Apples Crack? Gard. Chron. 1856, 
724. 1855. 
States that this due to Sfz/oce@a Pomi, the fructigenous form of He/mintho- 
sportum Pirorum, but does not recognize specific difference between the 
forms on apple and pear. 

Bizzozero, G. Fusicladium dendriticum var. minor, Sacc. Fl. Ven. Crittog. 
1:510. 1885. 
Follows Saccardo in giving form on apple as variety of that on pear. 

Blair, J. C. Spraying Apple Trees with special reference to Apple Scab Fun- 
gus. Ill. Agr. Exp. Stat. Bull. 54:181-204. 1899. [Illustr.] 
Gives results of spraying, directions for making fungicide, description of ma- 
chinery, etc. 

‘Bonorden, H. F. Fusicladium virescens. Handb Allg. Myk.:80. ¢.4, f 94. 
1851. 
Describes this as a new genus and species and says in part “Kommt in Garten 
auf veredelten Apfelbaumen vor.” Winter gives this as a synonym of pear 
scab and Bonorden’s figures certainly more nearly resemble that species than 
the one on the apple. 

Brefeld, O. Venturia ditricha f. Piri. Unter. Gesammt. Mykol heft. 10: 
221. 4.7,f.59, 60. 1891. 
Shows similarity of a stage produced from above fungus to the scab of pear 
and apple. 


128 BULLETIN NO. 67. [ December, 


Briosi and Cavara. /usicladium dendriticum (Wallr.) Fckl. Fung. par. no . 
140. 1892. y ; 

Give illustrations and specimens ofthis fungus together witha short description. 

Burrill, T. J. Notes on Parasitic Fungi. Agr. Rev: 86. , 1882. 

Gives an account of apple scab and two other fungi. 

Burriil, T. J. An Orchard Scourge.. Trans. Miss. Vall. Hort. Soc. 1:202-7. 
188 
Gives an account of apple scab and the damage caused in Illinois. 

Burrill, T. J. The Apple Scab Fungus. Trans. Ill. Hort. Soc. 1900 :86-97- 
1901, 
Writes a popular article on our present knowledge of apple scab. 

Butz, G. C. Apple Scab. Penn. Agr. Exp. Stat. Bull. 43:13, 16. 1898. 

Treats of apple scab and its prevention by spraying. 
Card, F. W. Apple Scab in Nebraska. Gard. & For. 8:28. 1895. . 
’ Thinks little scab found in this state is due to dry weather. 


Chester, F. D The Scab of the Apple and Pear. Del. Agr. Exp. Stat. Bull. 
3:6-7.. 1888. . 
Gives short note on above including preventive measures. 
Chester, F. D. Experiment in the Treatment of Apple Scab. Del. Agr. Exp. 
Stat. Bull. 29:18-24. 1895. 
Gives favorable results from spraying with Bordeaux mixture. : 
Chester, F. D. Experiment in the Treatment of Apple Scab. Del. Agr. Exp. 
Stat. Bull.°34:14-9. 1897. [Illustr.] 
Records favorable results from spraying with Bordeaux mixture. 


Chester, F. D. Continuation of the Work on the ‘Treatment of Apple Scab. 
Ann. Rep. Del. Agr. Exp. Stat. 11:27-30. 1900. 
Describes successful spraying experiments with Bordeaux mixture, 

Clark, J W. Spraying for the’Codling Moth and Apple Scab. Mo. Agr. Exp. 
Stat. Bull, 13:6., 1891. 
Reports favorable results from spraying with Bordeaux mixture. 

Close, C. P. Apple Scab. Utah Agr. Exp. Stat. Bull. 65:67-8. Igo0. 
Gives note on appearance of scab and remedy. 

Cobb, N. A. Apple Scab. Agr. Gaz. N.S. Wales 2:216, 492. 1891. 
Reports this on increase and suggests use of fungicides. 

Cobb. N. A. Apple Scab, “Tasmanian Black Spot.” Agr. Gaz. N.S. Wales 3: 
276-8: 1892. [Illustr.] i 
Gives short botanical account of the fungus and of the best fungicides for 


prevention. 
Collier, P. Apple Scab and Pear Scab. Ann. Rep. N. Y. Agr. Exp. Stat. 9: 
337-9. 1891. 


’ Describes effect of this on leaves and fruit and suggests preventives. 

Comes, O. Fusicladium dentriticum, Fck. Critt, Agr. :394. 1891. 
Gives short account of this fungus. 

Cooke, M. C. Spherella inegualis, Cke. Seem. Journ. Bot. 4:248-9, 1866. 
[Illustr.] ; 
Describes this as a new species on various hosts of the Pomacez. 

Cooke, M.C. Sphe@rella inequalis,Cke. Handb. Brit. Fungi:916. 1871. 
Describes this species and lists it on apple, pear, etc. 


190I.] APPLE SCAB. 129 


Cooke, M.-C. Sfilocea fomi, Fr. Grev. 2:64. 1873. 
Regards this as the fructigenous condition of Cladosporium dendriticum. 


Cooke, M. C. Fusicladium dendriticum, Fckl. Bull. Buff. Soc. Nat. Sci. 3; 198. 
1877. 
Lists it as occurring in the U. S. on apple leaves and fruit. 
Cooke, M. C. Apple Scab. Grev. 20:27-9. 1891. 
Gives synopsis of recent spraying experiments of U.S. Dept of Agr. 
Corbett, L. C. Apple Scab. W. Virg. Agr. Exp. Stat. Bull. 66:204-6. Ig00. 
[Illustr.] 
Gives characters of apple scab and best preventive treatment. 
Corbett, L. C The Value of sh gin eh W. Virg. Agr. Exp. Stat. Bull. 70: 354- 
5. Igoo. [Illustr.] 
Gives results of experiments showing time best to spray for scab. 


Costantin, J. Fusicladium. Les Mucedinees Simples : 69 - 71. 1888, 
Figures and gives short account of apple scab. 
Cuboni, G. Sulla forma ibernante del Fusicladium dendriticum. Bull. soc. bot. 
ital : 287-8. 1892. 
- Describes a hibernating condition or stroma found on twigs that under 
proper conditions of moisture and heat gave rise to the characteristic conidia. 


Curtis, M. A. Sfilocea Pomi, Fr. Curtis’ Cat. Plants N. Car:121. 1867. 
Lists as common on skins of apples. 

Detmers, Freda. Apple Scab. Ohio Agr. Exp. Stat. 49: 187-92. .1891. [Illustr.] 
Gives short description of apple scab fungus and its injury. 

Ellis, J. B. _Dothidea pomigena, Schw. N. A. Pyr:605. 1892. 

Says after examination of Schweinitz’ specimen that this is apparently the 
fructigenous form of Fusicladium dendriticum. A recent examination by 
the writer, however, shows this not to be the case. 

*Eriksson, J. Bidrag till kaennedomen om vara odlade vaxters sjukdomar, 
Medd, frau Kong]. Landtt. Akad. Exp. 1:61. 1885. 

Gives abstract in Bot. Centr. 

Eriksson, J. Der Schorf der Obstbaume. Bot. Centr. 26:345-7. 1886. 
Abstracts an article published by him the year before on scab fungus and 
damage caused by it in Sweden. 

Evans, W. H. AppleScab. Handb. Exp. Stat. Work :18. 1893. 

Gives short description of scab and means for its prevention. 

Fairchild, D. G. Treatment of Apple Scab at Brockport. Div. Veg. Path. U. 
S. Dep. Agr. Bull. 3:62. 1892. 

Records negative results from spraying with different fungicides because of 
absence of scab. 

Fairchild, D. G. Apple Scab. Div. Veg. Path. U.S. Dep. Agr. Bull. 6 543-4: 
1894. 

Cites various experiments where Bordeaux mixture was used against apple 
scab. 

Flagg, C. O. The Use of Fungicides in the Treatment of the Apple Scab. R. I. 
Agr. Exp. Stat. Bull. 15: 21-2. 1892. 

Quotes from Green as to methods and results of spraying. 


*References marked thus the writer has not seen. 


130 BULLETIN NO. 67. [ December, 


Frank, A. 8B. Fusicladium dendriticum, Fckl.  Pflanzenkr:587-9. 1880, 
[Illustr.] 
Gives a short description of this fungus. 

*Fries, E. Spilocea Pomi, Fr. Nov. Fl. Suec. 5:79. 1819. 
Names this fungus here for the first time rather than in Syst. Mycol. 

Fries, E. Spilocza. Syst. Orb. Veg. 1:198. 1825. 
Describes this genus and gives host as living apple. 

Fries, E. -Spzloc@a Pomi, Fr. Syst. Myc. 3:504. 18209. 
Describes the form of apple scab found on the fruit. 

Fries, E. Sfilocea epiphylla, Fr. Syst. Myc.3:504. 1829. 
Describes a fungus on leaves from France that to all appearance is leaf form 
of apple (and pear?) scab. 

Fuckel, L. Fusicladium dentriticum, (Wallr.) Symb. Myc :357. 1869. 
Re-names Cladosporium dendriticum, Wallr. as above. 

Galloway, B T. Fusicladium dendriticum. Ann. Rep. Mo. Hort. Soc. 29:91, 
267-99. 1886. 
Discusses scab and the use of the fungicides then known. 


Galloway, B. T. Apple Scab. Ann. Rep. U. S. Dep. Agr. 1889 : 405 - 12. 
1889. 

Reports upon spraying experiments conducted under his direction by Goff 
and Taft, eau celeste and ammoniacal solution copper carbonate giving best 
results of those tried. 

Galloway, B. T. Notes on the Fungus of Apple Scab. Mich. Agr. Exp. Stat. 
Bull. §9 :28-9. 1890. [Illustr.] 

Gives a brief description. 

Galloway, 8B T. Apple Scab. Ann. Rep. U. S. Dept. Agr. 1891 : 363. 1802. 
Gives a brief description of spraying experiments conducted under his di- 
rection by Goff, Bordeaux mixture proving more efficient than copper car- 
bonate. 

Galloway, B. T. Experiments in the Treatment of Apple Scab in Wisc: Dive 
Veg. Path. U. S. Dep. Agr. Bull. 3: 31-6. 1892. 

Reports more fully experiments of Goff in 1891, Bordeaux mixture proving 
most efficient. 

Galloway B. T. and Southworth, E. A. Treatment of Apple Scab. Journ. Myc. 
5:210-14. 1880. 

Gives results of spraying experiments conducted in Wisc. and Mich. with six 
‘different fungicides of which eau celeste and amm. sol. cop. carbonate gave 
best results. 

Garman, H. The Apple Scab Fungus. Ann. Rep. Ky. Agr. Exp. Stat. 2: 46-9. 
1889. [Illustr.] 

Gives description of fungus and discusses different fungicides. 

Garman, H. Apple Scab. Ky. Agr. Exp. Stat. Bull. 44:25-6. 1893. 
Notes favorable results from spraying with Bordeaux mixture. 

Garman, H. Apple Scab. Ann. Rep. Ky. Agr. Exp. Stat.6:53. 1894. 

Notes very favorable results from spraying a Janet apple tree with Bordeaux 
mixture. 

Goff, E.S. An Experiment for the Prevention of Apple Scab. Ann. Rep. N. Y. 
Agr. Exp. Stat. 4:260. 1886. 


1901.] APPLE SCAB. i) ae 


Gives favorable results from spraying crab-apple tree with hyposulphite of 
soda. 


Goff, E. S. Hyposulphite of Soda as a Preventive of Scab on the Apple and Pear. 
Ann, Rep. N. Y. Agr. Stat.6:117-8. 1887. 
Notes very beneficial results from spraying parts of a evabe apple and pear 
tree. 


Goff, E. S. Experiments in Treatment of Gooseberry Mildew and Apple Scab. 
Journ, Myc. 5:35-7. 1889. 
Gives results of spraying against apple scab with several fungicides. 


Goff, E.S. Treatment of Apple Scab. Journ. Myc. 6:19-21. 1890. 
Recommends the use of amm. sol. cop. carbonate. 


Goff, E. S. Report on the Treatment of Apple Scab. Sec. Veg. Path. U. S. Dep. 
Agr. Bull. 11: 22-8.. 18g0. 

Gives results of spraying with different fungicides of which amm. carb. of 
copper proved most effective. 

Goff, E.S. Prevention of Apple Scab, Fusicladium dendriticum, Fckl. The 
Prairie Farmer 62:246. 1890. 
Describes scab briefly and also the use of fungicides to prevent it. 

Goff, E. S. Prevention of Apple Scab. Wisc. Agr Exp. Stat. Bull. 23:1- 11. 
1890. [Illustr.] 

Gives description of scab and results of spraying experiments carried on 
under direction of U. S. Dep. Agr., recommending amm. sol. cop. carbonate. 

Goff, E. S$. Experiment in the Treatment of Apple Scab. Journ. Myc. 7:17- 
22. 1891. 

Reports favorably on amm. sol. cop. carbonate and amm. cop. sulphate. 
Goff, E. 5. Experiment in the Treatment of Apple Scab. Ann. Rep. Wisc. 
"Agr. Exp. Stat. 8: 160-1. 1892. 

Summarizes results of spraying experiments conducted in 1890. 

Goff, E. S. Preventive Treatment for Apple Scab, etc. Wisc. Agr. Exp. Stat. 
Bull. 34:34-7. 1893. 

Recommends Bordeaux mixture. 

Goff, E. S. Experimental Treatment for Apple Scab. Ann. Rep. Wisc. Agr. 
Exp. Stat. 9: 264, 270. 1893. [Illustr.] 

Summarizes the results of spraying experiments conducted in Wisconsin. 

Goff, E. S. The Apple Scab and its Prevention. Ann. Rep. Wisc. Agr. Exp. 
Stat. 10:228. 1894. [Illustr.] 

Gives noteon scab and results of spraying experiments conducted during 
several years especially those of 1892 and recommends Bordeaux mixture. 


Goethe, R. Weitere Beobachtungen ueber den Apfel und Birnenrost. Gar- 
tenflora :293-9. 1887. 
Notes the relationship of Fusicladium stage of scab on apples and pears to 
mature stage on the dead leaves. 

Goethe, R. Zur Bekampfung der Apfelrostes. Gartenflora 37: 263. 1888. 
[bid 38.:241. 1880. 
Treats of the use and strength of Bordeaux mixture as fungicide for apple 
scab. 

Green, W. J. Spraying to Prevent Apple Scab. Ohio Agr. Exp. Stat. 4° :193- 
212, 1891. [Illustr.] 


132 BULLETIN NO. 67. [ December, 


Reports favorable results from spraying with Bordeaux mixture (4 lb. cop. 
sulf., 4 lb. lime, 50 gal. water). 


*Green, W. J. Fruit Notes. Ann. Rep. Ohio St. Hort. Soc. 31:11-2. 1898. 
Shows very beneficial results from spraying with Bordeaux mixture against 
scab. 

Halsted, B. D. Decays of Mature Apples. Ann. Rep. N. J. Agr. Exp. Stat. 14: 
369-70. 1894. 

Gives brief note on appearance of apple scab. 

Halsted, B. D. /usicladium dendriticum, Ann. Rep. N. J. Agr. Exp. Stat. 15: 
324. 1895. 

Notés scab as abundant in New Jersey. 

Harvey, F.L. Apple Scabor Black Spot. Ann. Rep. Me. Agr. Exp. Stat. 18882 : 
149-51. 1889. 

Gives short account of apple scab and means of prevention by spraying. 

Harvey, F.L. Apple Scab. Ann. Rep. Me. Agr. Exp. Stat. 1889 :182-4. 1890. 
{Illustr.] 

Gives notes on the spraying experiments conducted by U. S. Dep. Agr. 


Hatch, A. L. Experiments in Treating Apple Scab. Journ. Myc. 7:26. 1891. 
Speaks of necessity of early spraying and suggests diluter solutions than then 
used. R 

Henderson, L. F. Avple Scab in the Potlatch. Idaho Agr. Exp. Stat. Bull. 20: 
79-95. 1899. 

Reports favorable results from the use of Bordeaux mixture. 

Hoffmann, H. Cladosporium dendriticum. Index Fung :37. 1863. 
Gives reference to scab under this name. 


Hoskins, T. H. Orchard Spraying. Gard. & For. 5:371. 1892. 
Speaks of need of selection to obtain more hardy variety of apple against 
scab. 
Jones, L. R. The Prevention of Apple and Pear Scab by Spraying. Ann. Rep. 
Verm. Agr. Exp, Stat. 5: 132-3. 1892. 
Reports somewhat favorable results from spraying Greening apples with Bor- 
deaux mixture and amm. sol. cop. carbonate. 
Jones, L. R. Apple and Pear Scab. Verm. Agr. Exp. Stat. Bull. 28: 30-4. 
1892. 
Reports strong Bordeaux mixture more effective than amm. sol. cop. car- 
bonate but injuring the foliage somewhat. 


Jones, L. R. Apple Scab. Ann. Rep. Verm. Agr. Exp, Stat. 6:82-3. 1893. 
States that spraying experiments were failures due to excessive rains. 


Jones, L. R. Apple and Pear Scab. Verm. Agr. Exp. Stat. Bull. 44 : 83-93. 
1894. [Illustr.] 

Describes scab and gives favorable results from spraying with Bordeaux 
mixture. 

Jones, L. R, and Orton, W. A. Spraying for the Prevention of Apple Scab 
in 1897. Ann. Rep. Verm. Agr. Exp. Stat. 11: 195-8. 1898.  [Illustr.] 
Report very favorable results from spraying with Bordeaux mixture and show 
‘that sprayed trees hold fruit better. 

Jones, L. R. and Orton W. A. Spraying for the Prevention of Apple Scab. 
Ann. Rep. Verm. Agr. Exp. Stat. 12:156-9. 1899. 

Report favorable results from the use of Bordeaux mixture. 


I901.] APPLE SCAB. 133 


Keffer, C. A. Spraying Apple Trees. Mo. Agr. Exp. Stat. Bull. 27:1-24. 
p 1894. > 
Reports, as result of numerous experiments, Bordeaux mixture as largely 
preventing apple scab. 
Kinney, L. F. The Scabof Apple and Pear. Ann. Rep. R. I. Agr. Exp. Stat. 
7:185-7. 1895. ([Illustr.] 
Gives brief report on nature of scab. 
Lamson, H. H. Spraying against Pear and Apple Scab. Ann. Rep. N. H. Coll. 
Agr. 20:217-8, 238-9. 1892. 
Gives short description of scab and reports favorable results from. spraying 
with Bordeaux mixture and amm. sol. cop. carbonate. 
Lamson,. HH. Some Fungus Diseases of Plants and Their Treatment. N. H. 
Agr. Exp. Stat. Bull.9:7-11. 1894. [Illustr.] 
Describes scab and gives favorable results from spraying with Bordeaux 
mixture, 
Lamson, H.H. Spraying experiments in 1894. N. H. Agr. Exp. Stat, Bull. 27: 
5-7. 1895. 
Reports favorable results from use of Bordeaux mixture 
Lindan, G. Venturia chlorospora (Ces.) Karst. Die Nat. Pflanzenf. 1: 431. 1897. 
Mentions Fusicladium dendriticum, Wallr. as stage of above fungus. 
Link, H. F. Sftloc@a Pomi. Linn. Sp. Plant. 67: 86. 1825. 
Gives a description of the fructigenous form of the apple scab. 
Lodeman, E. G. Spraying Apple Orchards in a wet Season. Corn. Agr. Exp. 
Stat. Bull. 48:265-98. 1892. [Illustr.] 
Gives results of spraying with Bordeaux mixture, a table of varieties most and 
least likely to scab, and the chemistry of Bordeaux mixture. 
Lodeman, E.G. The Profits of Spraying Apple Orchards. Corn. Agr. Exp, 
Stat. Bull. 60:257-79. 1893. 
Gives results of spraying experiments chiefly with fungicides against apple 
scab. 
Lodeman, &. G. The Spraying of Orchards. Corn. Agr. Exp. Stat. Bull. 86: 
105-25. 18095. 
Gives suggestions and results of spraying apples chiefly against scab. 
Macoun, W. T. Black Spot Fungus or Scab. Dep. Agr. Cent. Exp. Farm, Ot- 
tawa, Can. Bull. 37 ; 67-8. Igol. 
Notes this fungus as being very troublesome during recent years, etc. 
Massee, G. Apple Scab. A Text Book of Plant Diseases : 302 - 4, 435. 1899 
[Illustr.] 
Gives a short botanical description of this fungus together with preventive 
measures. 
Maynard, S. T. Fungicides and Insecticides on the Apple, Pear, and Plum. 
Mass. Hatch. Agr. Exp. Stat. Bull, 11:12-6. 1891. 
Reports various spraying experiments which so far as preventing apple scab 
were not very successful. 
McCarthy, G. Apple Scab. N.C. Agr. Exp. Stat. Bull. 76:15. 1891. 
Gives short note on scab and means for prevention. 
McCarthy, G. Apple Scab. N.C. Agr. Exp. Stat. Bull. 92 :87-8. 1893. 
Gives general information concerning scab and list of varieties most and 
least liable to attack. 


134 BULLETIN NO. 67. [ December, 


Munson, W. M.. Spraying Experiments. Ann. Rep. Me. Agr. Exp. Stat. 
1891 :110-8. 1892. [Illustr.] 
Gives account of scab and results of favorable spraying experiments with eau 
celeste and amm. sol. cop. carbonate. 


Munson, W. M. Spraying Experiments. Ann. Rep. Me. Agr, Exp. Stat. 
1892 :92,-8. 1893. 
Reports favorable results from spraying with eau celeste against scab. 


Munson, W. M. _Notes on Spraying Experiments. Ann. Rep. Me. Agr. Exp. 
Stat. 1893?:124-8. 1894. [Illustr.] 
Gives favorable results from spraying with Bordeaux mixture against scab. 
Niess!l, G.V. Didymospheria inegualis (Cke.) Nssl. Rab. Fung. eur. no. 2663. 
1881. 
Changes to above name from Spfherella inequalis. Cke. 


Niessl, G. V. Bemerkung ueber Venturia inegualis, Cke. und verwandte 
Formen. Hedw. Beibl. 37:1-2. 1898. 
Criticises Aderhold for placing above species under genus Venturia merely 
because of presence of bristles around ostiolum. 

Pammel, L. H. Apple Scab and Leaf Blight. Prairie Farmer. 57:746. 1885; 
[Illustr.] 
Gives abstract of Trelease’s article. : 


Pammel, L.H. Apple Scab. Ia. Agr. Exp. Stat. Bull. 13 : 48-9. ao [Illustr.] 
Gives cop. carbonate as fungicide for this disease. 

Peck, C. H. Sfpilocea Pomi, Fr. N. Y. St. Mus. Nat. Hist. 23:55. 1872. 
Reports scab common on apples in N. Y. in 1869. 

Peck, C. H. Fusicladium dendriticum, Wallr. N. Y. St. Mus, Nat. Hist. 34: 32 - 
3. 1883. 
Gives short account of above including with it forms on pear, etc. 

Persoon, C. H. Fumago Mali, Myc. Eur. 1:9. 1822. 
Gives brief description of above fungus which may possibly be the apple scab 

Piper, C. V. AppleScab. Wash. Agr. Exp. Stat. Bull. 8:138. 1893. 
Writes briefly about apple scab and its prevention by spraying. 

Powell, G. H. The Apple Scab. Gard. and For. 7:297. 1894. 
Gives list of varieties most and least affected by scab as determined at Corn. 
Exp. Stat. 

Roumeguere, C. Fusicladium dendriticum forma microsperma. Roum. Fungi. 
sel. exs. n.5592. 1890. 
Describes briefly this new form of which a specimen is given. 

Saccardo, P. A. Fusicladium dendriticum (Wallr.) Fokl.. var. minor Sacc. 
Fung. Ital. £782. 1881. 
Gives form on apple as variety of that on pear. 

Saccardo, P.A. Fusicladium dendriticum(Wallr.) Fckl. Syll. Fung. 4 :345. 1886. 
Gives botanical description of above species. 

Saccardo, P. A. Fusicladium dendriticum (Wallr.) Fckl. var. Soraureri (Thuem.) 
Sacc. Syll. Fung. 4:346. 1886. 
Reduces Thuemen’s WVaficladium Soraueri to variety of apple scab. 

Schroeter, J. Fusicladium dendriticum, (Wallr.) Kryp. Fl. Schl. 3?: 352. 
1894. 
Describes scab on apple and pear as a conidial stage of Venturia chlorospora. 


ous” + hy oa _* 2 a P86 + > 5 ain a . ¥ 
Pa sigy Shama ta pe ; ? . - : 


I90I.] , APPLE SCAB. 135 


Schweinitz, L. D. de Spzlocea fructigena aut Pomi, Lk. Syn. F. N, A.:297. 
1834. 
Reports above not rare on Newton Pippin; seems to have originated the 
specific name “/ructigena.” 


Scribner, F. Lamson. Fungous Diseases of Plants. Ann. Rep. U. S. Dept. 
Agr. 1885: 81. 
Suggests raking and burning of leaves as of possible benefit in preventing 
apple scab. 


Scribner, F. Lamson. AppleScab. Ann. Rep. U. S. Dep. Agr. 1887: 341-7. 
1888. [Illustr.] 
Gives a botanical account of scab, also gives literature and recommends 
winter treatment with iron sulphate and early spring spraying with Bordeaux 
mixture, 


Scribner F. Lamson, Apple Scab. Tenn. Agr. Exp. Stat. Special Bull. C :6 
1890. 
Recommends certain fungicides. 

Scribner, F. Lamson. Apple Scab. Fungus Diseases of the Grape and Other 
Plants :90-6. 1890. [Illustr.] 
Gives short botanical account of the fungus and methods for combating it. 


*Scribner, F. Lamson. Apple Scab and its Treatment. Orch. & Gard. 12: 113. 
1890. 
Writes a general article on above subject. 

Secretan, L. Sfzlocea pomi. Myc. Suisse: 594. 1833. 
Questions whether Fries’ specimen is really distinct from Epochnum. 


Selby, A.D. Apple Scab. Ohio Agr. Exp. Stat. Bull. 79 : 129-32. 1897. [Illustr.] 
Gives short description of apple scab and assigns it as the cause of the drop- 
ping of very young apples. 


Selby, A.D. Apple Scab. Ohio Agr. Exp. Stat. Bull. 111 :95-115, 1899. 
Gives results of various spraying experiments carried on at different times by- 
persons in Ohio. 


Smith, E.F. Apple Scab. Journ. Myc. 7: 373-4. 1894. : 
Speaks of 1892 as unusually bad year for scab in western N. Y. and south- 
western Mich. because of wet spring. 


Sorauer, P. Ueber die Entstehung der Rostflecken auf den Fruchten der Ker- 
nobstes, *Vers. deutsch. Naturf. u. Aerzte. 1874:84-5. [Bot. Zeit: 50-1. 
1875.] 

Gives botanical account of apple scab on leaves and fruit. 

Sorauer,P. Die Entstehung der Rostflecken, auf-Aepfeln und Birnen. Monats- 
schrift Ver. Beford. Gart. Konigl. Preuss. Staaten 18:5-15. 1875. [Illustr.] 
Gives a description of scabs of apple, pear, etc. 


Sorauer, P. Fusicladium dendriticum. Die Obstbaumkrankheiten : 100 - 3. 
1882. 
Gives account of the gross and microscopical appearance of scab on leaves 
and fruit. 


Sorauer, P. Die Rostflecke der Aepfel und Birnen. Handbuch Pflanzenkrank- 
heiten : 392. 1886. 
Describes apple scab briefly. 


136 BULLETIN NO. 67. (December, 


Sorauer, P. Fusicladium dendriticum. Die Schaden Kulturpflanzen : 224. 1888. 
Gives short note on this fungus. 

Sprague, C.J. Spilocea fructigena, Schw. Proc. Soc. Nat. Hist. Bost. 5 : 320. 
1856, 

Lists this from New England but does not give host. 

Stewart, F.C and Blodgett, F. H. Scab. N. Y. Agr. Exp. Stat. 167 : 283. 1899. 
Note occurence on twigs of Lady apple. 

Stinson, J. T. Apple Scab, etc. Ark. Agr. Exp. Stat. Bull. 21:57-8. 1892. 
Gives directions for spraying with Bordeaux mixture. 

Stinson, J. T. Apple Scab. Ark. Agr. Exp. Stat. Bull. 26 : 23 - 33., 37-44. 1894, 
Gives favorable results from spraying with Bordeaux mixture and notes on 
‘damage caused by scab over the state. 

Stinson, J.T. Spraying Experiments. Ark. Agr. Exp. Stat. Bull.39: 20-1. 1896. 
Notes that spraying experiments were not profitable because of the lack of 
scab that year. 

Streinz, W. M. Nomenclator fungorum : 187, 280, 308. 

Gives Fumago mali Pers. and Helminthosporium pyrorum Tib. as synonyms 
Of Cladosporium dendriticum, Wallr. 
Sturgis, W. C. Scab. Conn. Agr. Exp. Stat. Bull. 111: 3-4. 1892. 
Describes briefly scab and its prevention by spraying. 
Sturgis, W. C. Scab. Conn. Agr. Exp. Stat. Bull. 115:3-4. 1893. 
Gives short note on apple scab. 


Sturgis, W. C. Spraying for Scab of Apples and Pear. Ann. Rep* Conn. Agr. 
Exp. Stat. 17:72. 1893. 
Gives results of spraying experiments including winter and summer treatments. 


Sturgis, W. C. Fusicladium dendriticum (Wallr. Fckl) Ann. Rep. Conn. 
Agr. Exp. Stat. 1900 : 258. 1900. 
Gives a few references to literature. , 

Taft, L.R. Report on Experiments with Remedies for the Apple Seab. Sec. 
Veg. Path. U. S. Dep. Agr. 11: 30-8, 1890. 
Gives experiments of spraying with different fungicides of which modified 
eau celeste and amm. cop. carbonate gave best results. 

Taft, L.R. Report on Experiments .made in 1889 in the Treatment of Apple 
Scab in Michigan. Mich. Agr. Exp. Stat. Bull. 59: 30-42. 1890. 
Obtained best results from use of modified eau celeste. 

Taft, L.R. Apple Scab. Mich. Agr. Exp. Stat. Bull. 83:12-4. 1892. [Illustr.] 
Presents a short description of the fungus with recommendations for Si hiai 

Taft, L. R. and Davis, G.C. Apple Scab. Mich. Agr. Exp. pith Bull. :19- 


21. 1895. [Illustr.] 
Write briefly about scab and recommend use of Bordeaux mixture. 


Thuemen, F. v. Napicladium, eine neue Hyphomyceten-Gattung. Hedw. 14: 


3-4. 1875. 
Describes scab on apple fruit as a new genus. 

Thuemen, F. v. Nafpicladium Sorauert, Thuem. Myc. Uni. no. 91. 1875. 
Gives specimen and description of his new genus. 

Thuemen, F.v. Ueber einige besonders beachtenswerte durch parasitische Pilze 
hervorgerufene Krankheiten der Apfelbaumblatten. Zeit. Pflanzk. 1: 167. 
1891. 


1901, | APPLE SCAB, 137 


s 
Discusses apple scab and gives /. dendriticum var. Soraueri and Napicla- 
dium Soraueri as synonyms, 


Tillinghast, J. A. and Adams, G. & Apple Scab. R. I. Agr. Exp. Stat. Bull. 


52:20-I. 1899. 
Describe appearance of apple scab and suggest remedy. 


Trelease, W. The Apple Scab and Leaf Blight. Ann. Rep. Wisc. Agr. Exp. 
Stat. 1:45-56. 1884. [Illustr.] 
Gives extended account of scab, varieties attacked, and recommends raking 
together and burning leaves. 


Trelease. W. Fusicladium dendriticum(Wallr.) Prel. List. Par. Fungi. Wis : 15. 
1884. yi : 
Lists this as very destructive and on following hosts, Pyrus Malus, P. coro- 
naria, P. pruntfolia. 

Wallroth, F. G. Cladosporium dendriticum. F|. Crypt. Germ. 12: 169. 1833. 

Describes this as a new species on apple with questioning reference to identity 
with Persoon’s Fumago Mali. 


Weed, C. M. Apple Scab. Ohio Agr. Exp. Stat. 27:188. 1889. (Illustr.) 
Reports injury to fruit from spraying with Bordeaux mixture. 


Whitten, J. C. The Apple Scab. Mo. Agr. Exp. Stat. Bull. 31:3,6-7, 11 - 16. 
1895. 
Reports favorable results from spraying with Bordeaux mixture. 

Williams, T. A. Apple Scab. S. D. Agr. Exp. Stat. Bull. 35:79. 1893. 
Gives short note on this subject. 


Winter, G. Ueber Wapicladium Sorauert, Thuem. Hedw. 14:35-6. 1875. 
Shows that above fungus is not distinct from Fusicladium dendriticum 
(Wallr.) 


Winter, G. Venturia inegualis, Wint. .Thuem. Myc. uni. no. 1544. 1880. 
Gives this name for first time to specimens on apple leaves. 


EXPLANATION OF ILLUSTRATIONS. 


Fig. 1. Neglected orchard in which scab abounds. 


Fig. 2. Sample twig from above orchard showing presence of scab on leaves and 
fruit. 

Fig. 3. Orchard in which scab is kept in check by proper spraying, pruning and 
cultivating. 

Fig. 4. Apple leaves showing scab colonies on upper and lower surfaces. 

Fig. 5. Apples showing scabby spots. 

Fig. 6-11. Transverse sections of apple leaves infected with scab, showing sub- 
cuticular mycelium, development of spores and the lengthening of conidio- 
phores with advance of season; a, parenchymatous cells of leaf; b, epidermal 
cells of leaf; c, cuticle of epidermis; d, subcuticular mycelium of scab; e, 
conidiophores of scab; f, scab spores. Fig. 6 shows scab on lower surface of 
leaf gathered May 3; fig. 7, on upper surface of leaf gathered May 27; fig. 
8-9, same date as fig. 7, but spores further developed ; fig. 10, on upper sur- 
face of leaf gathered June 23; fig.’11, on lower surface of leaf gathered Octo- 
ber I. 

. ig. 12-15. Sections through scab colonies on apples; a, parenchymatous cells; 
b, injured parenchymatous cells forming sort of corky layer; c, cuticle; d, 
subcuticular mycelium ; e, conidiophores ; f, spores. Fig. 12 shows scab on 
fruit gathered June 1; fig. 13, 14, gathered June 23; fig. 15, stored over 

- winter, 


138 BULLETIN NO. 67. [ December, 


Fig. 16. Spores (a) and conidiophores (b) of scab scraped from apple leaf. 

Fig. 17, Germinating scab spore (a) showing mycelium developed in a culture of 
new apple leaf agar. ; 

Fig. 18. Mycelium developed from scab spores, showing granular contents, 
septa and manner of branching. 


Fig. 19. Sameas 18 but showing reticular’ character of protoplasmic contents 
often seenin young threads or ends of old ones, 

Fig. 20, Mycelium with loose spores and large circular swellings in threads 
probably due to violent osmotic action. Culture impure. 

Fig. 21-26. Artificial cultures of scab grown on various media in test tubes, (a) 
being check test tubes containing no growths. Fig. 21, slight growths on old 
apple leaves on moist cotton; fig. 22, on beef broth agar; fig. 23, on old 
apple leafagar; fig. 24, in beef broth; fig. 25, in gelatin; fig. 26, on beef 
broth corn meal in which it most nearly approaches its condition in nature. 

Fig. 27. Crushed perithecium of Venturia inequalis, showing (a) reticulated 
walls of perithecium, (b) asco-spores, (c) asci, c’ being an empty ascus. 

Fig. 28. Transverse section through old apple leaf of previous year, gathered 
May 28, and the embedded perithecium of Venturia neqgualis, showing latter - 
cut through at side near projecting neck with its characteristic bristles (d). 

Fig. 29. Same as Fig. 28 but showing a few of the spores still inside the asci. 

Fig. 30. Same as Fig. 28 but section through center of perithecium, spores more 
or less shrunken. 

Fig. 31. A group of swollen germinating spores of Venturia inegualis produc- 
ing granular, roe threads similar to those from scab spores. 

Fig. 32. Same as Fig. 31, but mycelial threads having reticular protoplasm. 

‘Fig. 33. Sterile mycelial threads of Venturia grown on new apple leaf agar. 

Fig. 34. Fertile mycelial threads of Venturia grown on new apple leaf, corn 
meal, (a) being one of the scab spores produced. 

Plate I. Germination and spore production of Fusicladium dendriticum: a, 
spores ; b, germ-threads ; c, mycelium. Fig. A, germination of spores after 
16 hours in water, showing character of young germ-threads and manner of 
emerging from spores. Fig. B, sterile mycelium of scab third day after 
transfer to beef broth, showing resulting spore production. Fig. C, same as 
fig. B, but cultures 24 hours older and spores disappearing through germina- 
tion. Fig. D, drop culture six days old of spores in apple leaf broth, show- 
ing manner in which spores are formed and crowded off by later ones; a’ one 
of the original spores. 

Plate II. Peculiar development of mycelial threads of Pusicladium dendriticum 
in various media under different conditions. Fig. A. peculiarly knobbed and 
enlarged tinted branches frequently developed on threads in cell cultures. 
Fig. B, sterile threads grown in apple leaf agar; a, young scarcely tinted 
threads; b, older, larger and deeper tinted-threads ; c, peculiar swelling. fre- - 
quently found in threads. Fig. C, peculiar knobbed threads (a) as in Fig. A, 
sending out more slender, hyaline threads (b). Fig. D, growth of scab mycelium 
(a) inside of cotton hair (b) showing rounded segments quite like the sub- 
cuticular mycelium. Fig. E, mycelium several months old grown on apple 
leaf agar, showing condensed spore-like condition of thread’s contents. Fig. 
F, a dried out culture on young apple kept over winter, showing same spore- 
like bodies asin Fig. E. . 

Plate III. Venturia inegua/is from old apple leaves. Fig. A, spores (a) in asci 
(b) b’ being a ruptured ascus with spores partially escaped. Fig, B, loose 

_spores. Fig. C, perithecium which had been placed in apple leaf broth 15 
hours, showing penetration of the enclosed germinating spores. Fig. D, ger- 
mination of spores after 15 hours in apple leaf broth ; a, spore not yet swollen; 
b, swollen germinating spore ; c, swollen spores germinating inside of ascus. 
Fig, C and D less highly magnified. Fig. E germination of spores within 24 
hours after placing in water; a spore; b, germ-thread. 

Plate IV. Venturia inegualis. Fig. A, germination of spores after 15 hours in 
apple leaf broth ; a, spores ; b, germ-threads. Fig. B, germination of spores 
after two days in beef broth, showing peculiar knobbed and enlarged ends. 
Figs. Aand B less highly magnified. Fig. C, similarto Fig. B but older culture 
a’ showing (a) two hours later. Fig. D, mycelium (a) forming true scab 
spores (b), b’ being spore which germinated after its formation in the new 
apple leaf broth. 


APPLE SCAB. 139 


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